1. Field of the Invention
The present invention relates to a method of and an apparatus for manufacturing a shaft, and more particularly to a method of and an apparatus for manufacturing an elongate shaft that is suitable for transmitting power.
2. Description of the Related Art
Heretofore, drive shafts in automobiles serve as a component of the drive line for transmitting power from the engine, i.e., for transmitting rotary motion from the engine as rotary drive power to the drive wheels. There have been demands in the art for drive shafts that are lower in weight for better vehicle gas mileage and higher in rigidity for less vibration and noise.
One method of manufacturing a lightweight shaft is disclosed in Japanese Laid-Open Patent Publication No. 11-247835. According to the disclosed method, as shown in FIGS. 17A and 17B of the accompanying drawings, an end 202 of a hollow circular tube 200 is pressed into a cavity 206 defined in a die 204 so that it is squeezed into a smaller diameter (see FIG. 17A). Thereafter, a mandrel 208 is pushed into the opening in the end 202 to squeeze the end 202 between the inner circumferential surface of the cavity 206 and the outer circumferential surface of the mandrel 208 (see FIG. 17B). After the end 202 of the hollow circular tube 200 has been machined, the other end of the hollow circular tube 200 is similarly machined, thereby producing a shaft.
Japanese Laid-Open Patent Publication No. 10-036937 discloses a method of manufacturing a highly rigid shaft of carbon steel processed by high-frequency quenching.
The shaft disclosed in Japanese Laid-Open Patent Publication No. 11-247835 is a hollow shaft which is of a small wall thickness and low mechanical strength. Accordingly, it is difficult for the disclosed method to simultaneously machine the ends of the hollow circular tube 200. The disclosed method cannot be used to reduce the number of machining steps and shorten the manufacturing time by simultaneously machining the ends of the hollow circular tube 200.
The shaft disclosed in Japanese Laid-Open Patent Publication No. 10-036937 has a high level of high surface hardness. The disclosed method finds it difficult to simultaneously machine both ends of a cylindrical solid rod on a lathe, and fails to reduce the number of machining steps and shorten the manufacturing time in manufacturing a shaft.